Generally, the two-way power supply system is made up of ORing diodes whose schematic diagram is shown in FIG. 1. D1 and D2 are used to isolate two ways power supply (more Oring Diodes are used for multi-way than two), however, because of the forward voltage drop of diode (0.8V for silicon diode, 0.4V for Schottky diode) which is unacceptable for the low voltage power supply circuit, so that the isolation ORing diode is unsuitable to the low voltage circuit. Meanwhile, the master power supply and the slave power supply could not be determined in the case. If the voltages of the two power supplies have a little difference, D1 and D2 would be “on” simultaneously.
In view of the drawback existing in the conventional two-way power supply system, the invention proposes a switching circuit for the master-slave feeding mode of the low voltage power supply.